Endogenous opioid system down-regulation during hibernation in amphibians

Craig W. Stevens, Paul D. Pezalla

Research output: Contribution to journalArticlepeer-review

15 Scopus citations


In late summer, Northern grass frogs, Rana pipiens, intraspinally administered dynorphin produces a potent, dose-dependent antinociceptive action as measured by the acetic acid test used to evoke a hindlimb wiping response. Surprisingly, in fall, frogs which have entered hibernation, intraspinal dynorphin produces no antinociception action. Intraspinal morphine shows a decreased effect in fall frogs while systemic morphine is equi-effective in summer and fall frogs. Immobilization stress, previously shown to be mediated by endogenous opioid systems in this amphibian, produces a robust increase in nociceptive thresholds in summer frogs while the nociceptive thresholds of fall frogs are unaffected by this procedure. Summer frogs adapted to cold room (4 °C) show a significant decrease in nociceptive thresholds, compared to cohorts kept at room temperature, and cold-adapted frogs returned to room temperature show a naloxone-attenuated increase in nociceptive threshold. Collectively, these data suggest that endogenous opioid systems in these northern frogs are down-regulated during fall hibernation.

Original languageEnglish
Pages (from-to)227-231
Number of pages5
JournalBrain Research
Issue number2
StatePublished - 14 Aug 1989


  • Antinociception
  • Dynorphin
  • Hibernation
  • Intraspinal
  • Morphine
  • Opioid
  • Rana pipiens
  • Stress


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